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Il "Groppino"


The name "Groppino" is nowadays often heard at the airfields to describe a simple, easy and unexpensive, therefore "basic" ultralight. In effect this ULM, presented for the first time at the 1994 Montegrappa Meeting in Bassano, fullfills exactly all these requirements.

Nando Groppo began in the 80s to import the yankee "Quicksilver" ultralights, from one of the first sport aviation factories in the world.
When economic difficulties of the american factory and the high and unfavourable dollar exchange rates made very difficult to pursue the import  of the Quicksilvers, Nando Groppo thought how to resolve the problem, introducing a new personal project for an ultralight that was possible to produce completely in Italy.

These are the real reasons why the "Groppino" came out as a "replica" of the Quicksilver, sharing the same simple construction, the easy piloting and the low price. On the other hand, year after year, the "Groppino" begun to look more and more different from his "brother" and nowadays it is a completely original ultralight.

Let's look at it in details.

The "Groppino" is a tubes & fabric, high wing, traditional configuration ultralight. This means braced wing, aerodinamic controls, tail surfaces with fixed and moving parts, tricycle gear. There are two side-by-side seats and the engine is in a pushing position. This allows an excellent visibility and the possibility to choose between a full "open" version (it's like flying on a trike) and a partially closed cockpit fairing, more suitable in cold situations.

The main cell is builded in 4130 steel, while the rest of the structure is in 6061 alluminium alloy. All the parts and brackets are made using digital control machines.
Two trapezoids connect the lower part, supporting the seats, to the keel made of a square 1 1/2 inches beam. Below, a square section tube goes forward to the double pedals and the nose wheel. Another square tube supports the landing gear, consisting in a 2024 alluminium alloy leaf spring. All the (metric) nuts & bolts are cadmium plated.

Connected to the cell, 6 tubes forming a net truss support the tail surfaces, while two beamed-section double struts (in 2 sections) support each wing.

Each wing has two spars. The front one is the leading edge and is builded with three concentric tubes for the hardest working parts of the wing. The rear spar is the back edge and is made by two concentric tubes. The double surface wing shape is mantained with a series of ribs with pre-shaped curve, inserted in proper pockets sawn in the DacronŽ coating, like in the best tradition of ultralight flight. The generous aileron lenght is 2/3 of the wing span and is hinged to the back edge tube.

We already talked about fixed and moving parts for the tail surfaces. In fact only the horizontal part is divided into elevator and stabilizer. On the contrary, there is not a fin and the rudder is a single surface. The tail surfaces are all together quite big, assuring a good control at the pretty low speeds of this plane.

The controls are transmitted to the aerodinamic surfaces by means of steel cables for the rudder, two "Bowden" cables for the ailerons and a steel stick for the elvator. The separated brakes control lies between the seats, consenting a full control of the machine to the passenger or pupil. The drum brakes are indipendent on the two wheels. There is a mechanical trim.

As we said before, the engine is in a pushing configuration, above the keel among the rear part of the wings. The engine mounting is dynefocal designed. This means that the silent-block connections converge towards the engine drive shaft, with a strong reduction of the vibrations. For its high reliability and simpleness the Rotax 503 is normally installed.

The fuel tanks are made of composites and are part of the seats back. They contain about 7 gallons, but it is possible to mount an auxiliary 8 gallons tank.

The machine weights 420 lbs empty. The cockpit fairing brings up the weight about 20 lbs more.

Test flight

Let us fly the "Groppino". The test is performed in June, on a machine with cockpit fairing and double ignition, double-carburettors Rotax 503 engine, wooden two-bladed prop, B reducer. With two passengers and fuel the extimated weight is 840 lbs.

The ignition is manual, with the usual snatch. Sitted and fastened, we taxi to the waiting point. The ground manouvres are simple, even if the turning radius is not a taildragger one, with a little help from the brakes it is possible to move easily.

Full throttle, we pull the yoke at 37 mph and we take off after a 110 yds run. The climbing rate is good (no variometer) and reached a safety altitude, we level at 5500 rpm with a GPS controlled cruise speed of 60 mph.

Let us try the stall. Without power, with two passengers, the stall arrives after the usual buffeting at 36 mph. The "Groppino" brings down the nose and slightly inclinates one wing, owing to the prop torque. The power-on stall comes at 31 mph. With the pilot alone, the stall without power lowers to 28 mph.

Piloting is overall extremely simple and the response to the controls coherent with the characteristics of these machines. The effort of the aileron control could be improved. The turn must be controlled with some "foot" to counteract the adverse yaw.

Approach and landing are within everyone's reach. At 44 mph the plane comes down quietly and flaring at 38 mph makes possible to touch on three wheels, getting at once full control of the direction. In 90-110 yds the plane stops even without applyng brakes.

Personally, I think that the "Groppino" is a really fun machine and very suitable for the school. Moreover, the price is today very competitive in relation to every other national or foreigner product.
When this flight test was done, about 50 machines were already sold, ant this is an interesting numbre for the italian market. Other ones were sold in France and Spain, promitting a favourable "export" line.

Equipment

The standard equipment is a Rotax 503 engine, B reducer, two-bladed wooden prop and a little panel with basic instrumentation. At request, the C reducer can be mounted, with three-bladed silenced carbonium prop.
The cockpit fairing is optional (even if it is requested by nearly all buyers), it consents a speed increase of about 10 mph and a real noteworthy sheltering from the wind.

A STOL version is produced too, reccomended for the hydro- and crop-spraying configurations. This version mounts a Rotax 582 engine with B reducer and has a single-surface wing. The hydro mounts floaters are produced by Scuola Italiana Volo.

Flavio Giacosa


For further information: groppo@groppo.it

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